Continuously variable transmissions and their control are described, for example, in European patent publication 0,451,887 and in U.S. Pat. No. 5,514,050. U.S. Pat. No. 5,514,050 describes the adjustment of the gear ratio in such a continuously variable transmission. In this context, the downhill travel of the vehicle is detected and the adjusting strategy is modified during a detected downhill travel. It is especially here provided that the driving state of downhill travel is determined and the road speed is detected and stored at the time point of the start of the downhill travel. The transmission is then continuously adjusted so that the determined speed is essentially maintained while utilizing the braking action of the motor.
As a rule, the internal combustion engine of a vehicle is operated at relatively low rpm in order to exploit the consumption advantages of a vehicle equipped with a continuously variable transmission. A precondition for this is a low transmission gear ratio close to a so-called overdrive. As a consequence of this low engine rpm, the engine braking action is slight during downhill travel and especially in overrun operation.